JP5195509B2 - Engine starting device and engine starting method - Google Patents

Description

  The present invention relates to an engine starting device and a starting method.

  Conventionally, after the engine start condition is satisfied, a field current is supplied to the motor. When the field current reaches a current that can generate a torque sufficient to start the engine, a three-phase alternating current is supplied to the motor. An engine starting system for starting the engine is known (see Patent Document 1).

JP 2005-127199 A

  However, the field current that can generate a torque sufficient to start the engine varies depending on various conditions. In the conventional technique, the field current threshold value is set with a margin in consideration of the fluctuation, and there is a problem that it takes time to start the engine.

An engine starter and an engine start method according to an aspect of the present invention supply a field current to a motor when the engine start condition is determined to be satisfied, and generate a torque sufficient for the field current to start the engine. If it is determined that the current is larger than the possible current, an armature current is supplied to the motor to start the engine, and a determination threshold value used for determining the field current is set based on the engine temperature. It is characterized by that. The determination threshold is a determination time for comparison with the elapsed time from the start of energization of the field current, and when the elapsed time from the start of energization of the field current exceeds the determination time, the field current is It is determined that a current sufficient to generate a torque sufficient for starting has become larger. The determination time is set based on the engine temperature.

When it is determined that the engine start condition is satisfied, the engine start device and the engine start method according to another aspect of the present invention supply a field current to the motor, and the field current provides a torque sufficient to start the engine. When it is determined that the current is larger than the current that can be generated, the armature current is supplied to the motor and the engine is started. Based on the temperature of the motor, a determination threshold value used for determining the field current is set. It is characterized by doing. The determination threshold is a determination time for comparison with the elapsed time from the start of energization of the field current, and when the elapsed time from the start of energization of the field current exceeds the determination time, the field current is The determination threshold value setting means sets a determination time based on the temperature of the motor. The determination threshold value setting means determines that the current is larger than a current that can generate a torque sufficient for starting.

  According to the present invention, the time required to start the engine can be shortened.

It is a block diagram which shows the structure of the engine starting apparatus in 1st Embodiment. 5 is a flowchart illustrating engine restart control during engine stop (idle stop) in the engine start device according to the first embodiment. It is a figure which shows the relationship between engine water temperature and threshold current. It is a flowchart which shows the engine restart control in an engine starting apparatus in 2nd Embodiment during an engine stop (idle stop). It is a figure which shows the relationship between the temperature of a motor, and threshold current. It is a flowchart which shows the engine restart control in an engine starting apparatus in 3rd Embodiment in an engine stop (idle stop). It is a figure which shows the relationship between engine water temperature, motor temperature, and threshold current. It is a flowchart which shows the engine restart control in an engine starting apparatus in 4th Embodiment in an engine stop (idle stop). It is a flowchart which shows the engine restart control in an engine starting apparatus in 5th Embodiment in an engine stop (idle stop). It is a flowchart which shows the engine restart control in an engine starting apparatus in 6th Embodiment in an engine stop (idle stop).

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. The present invention is applied to a so-called idle stop vehicle that automatically stops and restarts an engine at the time of temporary stop / start such as waiting for a signal.

-First embodiment-
FIG. 1 is a block diagram showing the configuration of the engine starter according to the first embodiment. The motor 5 is connected to the engine 1 by a belt 6 and functions as a belt-type starter that starts the engine 1 when restarting from an idle stop. In order to start the engine 1, a field current is supplied to the rotor of the motor 5 to raise the field, and then an armature current is supplied to the stator to output a desired torque for rotating the engine 1. To do. At this time, the armature current starts to flow after the field current becomes larger than the threshold current.

  The battery 3 supplies a current to the motor 5. The motor temperature sensor 2 detects the temperature of the motor 5 and outputs it to the ECU 4. The current sensor 8 detects a field current flowing through the rotor of the motor 5 and outputs it to the ECU 4. The engine water temperature sensor 7 detects the temperature of the cooling water of the engine 1 and outputs it to the ECU 4. Note that the engine starter according to the first embodiment may be configured without the motor temperature sensor 2.

  The ECU 4 performs general control of the engine 1 including idle stop control. In particular, the ECU 4 controls the field current and the armature current of the motor 5 in order to restart the engine 1 from a state where the vehicle is idle-stopped. A control method at the time of engine restart will be described later.

  The friction of the engine 1 varies depending on the temperature of the engine 1. For example, when the temperature of the engine 1 is lower than when the temperature of the engine 1 is high, the friction of the engine 1 is large. When the friction of the engine 1 is large, it is necessary to increase the output torque of the motor 5 in order to start the engine 1. For this reason, in the engine starting device in the first embodiment, a threshold current to be compared with the field current is set according to the temperature of the engine 1 in order to output a motor torque according to the engine friction.

  In the present embodiment, the temperature of the cooling water of the engine 1 is detected as the temperature of the engine 1, but the temperature of the engine oil may be detected or the temperature of the engine 1 itself may be detected. Good.

  FIG. 2 is a flowchart showing engine restart control during engine stop (idle stop). The ECU 4 starts the process of step S10 during the idle stop.

In step S10, it is determined whether a restart condition of the engine 1 is satisfied. For example, it is determined that the restart condition of the engine 1 is satisfied when at least one of the following (1) to (6) is satisfied.
(1) Engine water temperature <predetermined temperature (2) vehicle speed> predetermined vehicle speed (3) accelerator pedal opening> predetermined opening (4) air conditioner operation (5) battery SOC <predetermined SOC
(6) Brake master back negative pressure <predetermined negative pressure The threshold values in the above (1) to (6) are determined as follows, for example. When the engine water temperature is low, the catalyst temperature is low and the exhaust gas purification performance is poor. Therefore, when the engine water temperature falls below a predetermined temperature, the engine 1 is restarted. This temperature is obtained experimentally, and is 80 ° C., for example. When the vehicle speed increases or when the accelerator pedal depression amount exceeds a predetermined value, it is an indication of the driver's willingness to drive, so the engine 1 is restarted. For example, the predetermined vehicle speed is 2 km / h, and the predetermined opening is 2 deg. Since the power of the air conditioner is supplied from the battery 3, the engine 1 is restarted in order not to reduce the charge amount. Further, the engine 1 is also restarted when the SOC of the battery 3 decreases. The predetermined SOC is also obtained experimentally, for example 60%. Furthermore, even when the brake master back negative pressure is lowered, it can be determined that the driver has lifted his / her foot from the brake pedal, so the engine 1 is restarted in preparation for starting. The predetermined negative pressure is also obtained experimentally. For example, the predetermined negative pressure is 8 Mpa.

  If it is determined that the restart condition of the engine 1 is not satisfied, the process waits in step S10. If it is determined that the restart condition is satisfied, the process proceeds to step S20. In step S20, energization of the field current of the motor 5 is started. In step S30, the engine coolant temperature is acquired from the engine coolant temperature sensor 7.

  In step S40, a threshold current to be compared with the field current value is set based on the engine water temperature acquired in step S30. This threshold current is a current value that can generate a torque sufficient to start the engine 1.

  FIG. 3 is a diagram showing the relationship between engine water temperature and threshold current. As shown in FIG. 3, the threshold current is increased as the engine water temperature decreases. As described above, this is because the friction of the engine 1 increases as the engine water temperature decreases. That is, since the output torque of the motor 5 needs to be increased in order to start the engine 1 having a large friction, the threshold current to be compared with the field current value is increased.

  Here, by performing an experiment or the like in advance, the relationship between the engine water temperature and a field current (threshold current) capable of generating a torque sufficient to start the engine 1 is determined as shown in FIG. The table current is prepared in advance, and the threshold current is set by referring to the table data based on the engine water temperature acquired in step S30.

  In step S50, it is determined whether or not the field current detected by the current sensor 8 is larger than the threshold current set in step S40. If it is determined that the field current is equal to or less than the threshold current, the process waits in step S50, and if the field current becomes larger than the threshold current, the process proceeds to step S60.

  In step S60, energization of the armature current of the motor 5 is started. As a result, the rotational speed of the motor 5 gradually increases, the output torque increases, and the engine 1 starts.

  According to the engine starting device in the first embodiment, when it is determined that the engine starting condition is satisfied, a field current is supplied to the motor 5 and the field current generates a torque sufficient to start the engine 1. When it is determined that the threshold current is larger than the possible threshold current, the armature current is supplied to the motor 5 to start the engine 1, and the threshold current is set based on the temperature of the engine 1. As a result, the motor torque according to the engine friction can be output, so there is no need to set a threshold current to be compared with the field current with a margin, and cranking is started, that is, the engine is started. Can be fast.

  In particular, as the temperature of the engine 1 is lower, the threshold current is set larger, so that the motor 5 can generate a torque sufficient to start the engine 1 even at a low temperature start when the engine friction is large. 1 can be reliably started.

-Second Embodiment-
When the temperature of the motor 5 increases, the output torque decreases even under the same field current and armature current flowing through the motor 5. Therefore, in the engine starting device in the second embodiment, a threshold current to be compared with the field current is set according to the temperature of the motor 5. The configuration of the engine starter in the second embodiment is the same as that of the engine starter in the first embodiment shown in FIG. 1, but the engine water temperature sensor 7 may not be provided.

  FIG. 4 is a flowchart showing engine restart control during engine stop (idle stop) in the engine starter according to the second embodiment. Steps for performing the same processing as the processing in the flowchart shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted. The ECU 4 starts the process of step S10 during the idle stop.

  In step S400, the temperature of the motor 5 detected by the motor temperature sensor 2 is acquired.

  In step S410, a threshold current to be compared with the field current value is set based on the motor temperature acquired in step S400.

  FIG. 5 is a diagram showing the relationship between the temperature of the motor 5 and the threshold current. As shown in FIG. 5, the threshold current is increased as the motor temperature increases. This is because as described above, the motor output decreases as the motor temperature increases. That is, in order to increase the output torque of the motor 5, the threshold current to be compared with the field current value is increased.

  Here, a relationship between the motor temperature and a field current (threshold current) capable of generating a torque sufficient to start the engine 1 is determined by performing an experiment or the like in advance. The table data is prepared in advance, and the threshold current is set by referring to the table data based on the motor temperature acquired in step S400.

  If it is determined in step S50 that the field current detected by the current sensor 8 is larger than the threshold current set in step S410, the process proceeds to step S60, and energization of the armature current of the motor 5 is started.

  According to the engine starting device in the second embodiment, the threshold current to be compared with the field current is set based on the temperature of the motor 5, so it is necessary to set the threshold current with a margin. Thus, cranking can be started, that is, the engine can be started earlier.

  In particular, since the threshold current increases as the temperature of the motor 5 increases, the motor has sufficient torque to start the engine 1 even under conditions where the temperature of the motor 5 increases and the motor output decreases. The engine 1 can be started reliably.

-Third embodiment-
In the engine starting device in the third embodiment, a threshold current to be compared with the field current is set based on the engine water temperature and the temperature of the motor 5. The configuration of the engine starter in the third embodiment is the same as that of the engine starter in the first embodiment shown in FIG.

  FIG. 6 is a flowchart showing engine restart control during engine stop (idle stop) in the engine starter according to the third embodiment. Steps for performing the same processing as the processing in the flowchart shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted. The ECU 4 starts the process of step S10 during the idle stop.

  When the engine water temperature is acquired from the engine water temperature sensor 7 in step S30, the process proceeds to step S600. In step S600, the temperature of the motor 5 detected by the motor temperature sensor 2 is acquired.

  In step S610, a threshold current to be compared with the field current value is set based on the engine water temperature detected in step S30 and the motor temperature acquired in step S600.

  FIG. 7 is a diagram showing the relationship between the engine water temperature, the motor temperature, and the threshold current. The horizontal axis in FIG. 7 represents the engine water temperature, and the vertical axis represents the threshold current. As shown in FIG. 7, the threshold current increases as the engine water temperature decreases, and the threshold current increases as the motor temperature increases.

  Here, by performing experiments and the like in advance, table data defining the relationship between the engine water temperature and the motor temperature and the threshold current as shown in FIG. 7 is prepared in advance, and the engine water temperature acquired in step S30, and Based on the motor temperature acquired in step S600, the threshold current is set by referring to the table data.

  If it is determined in step S50 that the field current detected by the current sensor 8 is larger than the threshold current set in step S610, the process proceeds to step S60, and energization of the armature current of the motor 5 is started.

  According to the engine starting device in the third embodiment, since the threshold current to be compared with the field current is set based on the temperature of the engine 1 and the temperature of the motor 5, the threshold current has a margin. Therefore, it is not necessary to set, and the start of cranking, that is, the engine start can be accelerated. In this case, the threshold current corresponding to the states of both the engine 1 and the motor 5 is set as compared with the case where the threshold current is set based only on the temperature of the engine 1 or only on the temperature of the motor 5. Therefore, the torque sufficient to start the engine 1 can be more reliably generated by the motor 5, and the engine 1 can be started more reliably. Further, depending on the states of the engine 1 and the motor 5, cranking can be started earlier than when the threshold current is set based on only the temperature of the engine 1 or only the temperature of the motor 5. .

-Fourth embodiment-
In the first embodiment described above, energization of the armature current is started when the field current becomes larger than a threshold current that can generate a torque sufficient to start the engine 1. However, the relationship between the elapsed time from the start of energization of the field current and the field current value is obtained in advance, and the field current is greater than the threshold current based on the elapsed time from the start of energization of the field current. It can also be determined whether or not. This method is described below.

  The configuration of the engine starting device in the fourth embodiment is the same as that of the engine starting device in the first embodiment shown in FIG. 1, but a current sensor 8 for detecting a field current is provided. It can be omitted.

  In the first embodiment, as shown in FIG. 3, table data defining the relationship between the engine water temperature and a field current (threshold current) that can generate a torque sufficient to start the engine 1. Was prepared in advance. In the fourth embodiment, the relationship between the elapsed time from the start of energization of the field current and the field current value is obtained in advance, and based on this relationship, the engine water temperature and the start of energization of the field current are determined. Table data defining the relationship between the elapsed time and the determination time for comparison is prepared in advance. This table data includes, for example, the threshold current shown in FIG. It can be created by replacing with a determination time for comparison. Therefore, the relationship between the engine water temperature and the determination time is the same characteristic as the relationship between the engine water temperature and the threshold current shown in FIG. 3, and the determination time is lengthened as the engine water temperature decreases.

  FIG. 8 is a flowchart showing engine restart control during engine stop (idle stop) in the engine starter according to the fourth embodiment. Steps for performing the same processing as the processing in the flowchart shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted. The ECU 4 starts the process of step S10 during the idle stop.

  When the engine water temperature is acquired from the engine water temperature sensor 7 in step S30, the process proceeds to step S800. In step S800, based on the engine water temperature acquired in step S30, a determination time for comparison with the elapsed time from the start of energization of the field current is set. As described above, table data defining the relationship between the engine water temperature and the determination time is prepared in advance, and the determination time is set by referring to the table data based on the engine water temperature acquired in step S30. .

  In step S810, it is determined whether the elapsed time from the start of energization of the field current in step S20 is longer than the determination time set in step S800. If it is determined that the elapsed time since the start of energization of the field current has become longer than the determination time, it is determined that the field current has become larger than a current that can generate sufficient torque to start the engine 1. Then, the process proceeds to step S60, and energization of the armature current of the motor 5 is started.

  According to the engine starting device in the fourth embodiment, the start of cranking, that is, the engine starting can be accelerated as in the first embodiment. Moreover, since it is not necessary to provide the current sensor 8 for detecting the field current, the cost can be reduced.

-Fifth embodiment-
In the engine starting device in the second embodiment, a threshold current to be compared with the field current is set according to the temperature of the motor 5. In the engine starter according to the fifth embodiment, a determination time for comparison with the elapsed time from the start of energization of the field current is set according to the temperature of the motor 5.

  The configuration of the engine starter in the fifth embodiment is the same as that of the engine starter in the second embodiment, but the current sensor 8 for detecting the field current can be omitted. .

  FIG. 9 is a flowchart showing engine restart control during engine stop (idle stop) in the engine starter according to the fifth embodiment. Steps for performing the same processing as the processing in the flowchart shown in FIG. 4 are denoted by the same reference numerals, and detailed description thereof is omitted. The ECU 4 starts the process of step S10 during the idle stop.

  When the temperature of the motor 5 is acquired from the motor temperature sensor 2 in step S400, the process proceeds to step S900. In step S900, based on the motor temperature acquired in step S400, a determination time to be compared with the elapsed time from the start of energization of the field current is set.

  Here, based on the relationship between the motor temperature and the threshold current shown in FIG. 5 and the relationship between the elapsed time from the start of energization of the field current and the field current value, the temperature of the motor 5 and the determination time are Table data that defines the relationship is prepared in advance. The relationship between the motor temperature and the determination time is the same characteristic as the relationship between the motor temperature and the threshold current shown in FIG. 5, and the determination time is lengthened as the motor temperature increases. In step S900, the determination time is set by referring to the table data based on the motor temperature acquired in step S400.

  In step S910, it is determined whether the elapsed time from the start of energization of the field current in step S20 is longer than the determination time set in step S900. If it is determined that the elapsed time from the start of energization of the field current is longer than the determination time, the field current is greater than a threshold current that can generate sufficient torque to start the engine 1. After the determination, the process proceeds to step S60, and energization of the armature current of the motor 5 is started.

  According to the engine starter in the fifth embodiment, the start of cranking, that is, the engine start can be accelerated as in the second embodiment. Moreover, since it is not necessary to provide the current sensor 8 for detecting the field current, the cost can be reduced.

-Sixth embodiment-
In the engine starter according to the third embodiment, a threshold current to be compared with the field current is set based on the engine water temperature and the motor 5 temperature. In the engine starter according to the sixth embodiment, a determination time for comparison with the elapsed time from the start of energization of the field current is set according to the engine water temperature and the temperature of the motor 5.

  The configuration of the engine starter in the sixth embodiment is the same as that of the engine starter in the third embodiment, but the current sensor 8 for detecting the field current can be omitted. .

  FIG. 10 is a flowchart showing engine restart control during engine stop (idle stop) in the engine starter according to the sixth embodiment. Steps for performing the same processing as the processing in the flowchart shown in FIG. 6 are assigned the same reference numerals, and detailed description thereof is omitted. The ECU 4 starts the process of step S10 during the idle stop.

  When the temperature of the motor 5 is acquired from the motor temperature sensor 2 in step S600, the process proceeds to step S1000. In step S1000, based on the engine water temperature acquired in step S30 and the motor temperature acquired in step S600, a determination time to be compared with the elapsed time from the start of energization of the field current is set.

  Here, the engine water temperature and the temperature of the motor 5 are based on the relationship between the engine water temperature and motor temperature and the threshold current shown in FIG. 7 and the relationship between the elapsed time from the start of energization of the field current and the field current value. Table data that defines the relationship between and the determination time is prepared in advance. The relationship between the engine water temperature and the motor temperature and the determination time is the same characteristic as the relationship between the engine water temperature and the motor temperature and the threshold current shown in FIG. 7, and the determination is made as the engine water temperature decreases and the motor temperature increases. Increase time. In step S1000, the determination time is set by referring to the table data based on the engine water temperature acquired in step S30 and the motor temperature acquired in step S600.

  In step S1010, it is determined whether the elapsed time from the start of energization of the field current in step S20 is longer than the determination time set in step S1000. If it is determined that the elapsed time from the start of energization of the field current is longer than the determination time, the field current is greater than a threshold current that can generate sufficient torque to start the engine 1. After the determination, the process proceeds to step S60, and energization of the armature current of the motor 5 is started.

  According to the engine starting device in the sixth embodiment, the cranking can be started, that is, the engine can be started earlier as in the third embodiment. Moreover, since it is not necessary to provide the current sensor 8 for detecting the field current, the cost can be reduced.

  It goes without saying that the present invention is not limited to the first to sixth embodiments described above, and includes various modifications and improvements that can be made within the scope of the technical idea thereof.

DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Motor temperature sensor 3 ... Battery 4 ... ECU
DESCRIPTION OF SYMBOLS 5 ... Motor 6 ... Belt 7 ... Engine water temperature sensor 8 ... Current sensor ECU4, S10 ... Engine starting condition establishment determination means Battery 3, ECU4, S20 ... Field current supply means Current sensor 8 ... Field current detection means ECU4, S50 or S810 or S910 or S1010 ... determining means Battery 3, ECU4, S60 ... armature current supply means Engine water temperature sensor 7, S30 ... engine temperature detecting means ECU4, S40 or S410 or S610 or S800 or S900 or S1000 ... decision threshold setting Means Motor temperature sensor 2, S400, S600: Motor temperature detecting means

Claims (9)

An engine starting device for starting the engine by transmitting power of a motor to the engine,
Engine start condition satisfaction determining means for determining whether the engine start condition is satisfied;
When it is determined that the engine start condition is satisfied, field current supply means for supplying a field current to the motor;
Field current detection means for detecting the field current;
Determining means for determining whether or not the detected field current is larger than a current capable of generating a torque sufficient to start the engine;
Armature current supply means for supplying an armature current to the motor when it is determined that the field current is greater than a current capable of generating a torque sufficient to start the engine;
Engine temperature detection means for detecting the temperature of the engine;
A determination threshold value setting means for setting a determination threshold value used when the determination means determines based on the detected temperature of the engine;
Equipped with a,
The determination threshold is a determination time for comparing with an elapsed time from the start of energization of the field current,
When the elapsed time from the start of energization of the field current exceeds the determination time, the determination means determines that the field current is larger than a current that can generate a torque sufficient to start the engine. Is,
The determination threshold setting means sets the determination time based on the engine temperature.
An engine starter characterized by that.   2. The engine starter according to claim 1, wherein the determination threshold value setting unit sets the determination time longer as the temperature of the engine is lower. Motor temperature detecting means for detecting the temperature of the motor,
3. The engine starter according to claim 1, wherein the determination threshold value setting unit sets the determination time based on a temperature of the engine and a temperature of the motor.   4. The engine starter according to claim 3, wherein the determination threshold value setting unit sets the determination time longer as the engine temperature is lower and as the motor temperature is higher.   The engine start according to any one of claims 1 to 4, wherein the engine temperature detecting means detects the temperature of engine cooling water or the temperature of engine oil as the temperature of the engine. apparatus. An engine starting device for starting the engine by transmitting power of a motor to the engine,
Engine start condition satisfaction determining means for determining whether the engine start condition is satisfied;
When it is determined that the engine start condition is satisfied, field current supply means for supplying a field current to the motor;
Field current detection means for detecting the field current;
Determining means for determining whether or not the detected field current is larger than a current capable of generating a torque sufficient to start the engine;
Armature current supply means for supplying an armature current to the motor when it is determined that the field current is greater than a current capable of generating a torque sufficient to start the engine;
Motor temperature detecting means for detecting the temperature of the motor;
A determination threshold value setting means for setting a determination threshold value used when the determination means makes a determination based on the detected temperature of the motor;
Equipped with a,
The determination threshold is a determination time for comparing with an elapsed time from the start of energization of the field current,
When the elapsed time from the start of energization of the field current exceeds the determination time, the determination means determines that the field current is larger than a current that can generate a torque sufficient to start the engine. Is,
The determination threshold setting means sets the determination time based on the temperature of the motor;
An engine starter characterized by that.   The engine starter according to claim 6, wherein the determination threshold setting means sets the determination time longer as the temperature of the motor is higher. An engine starting method for starting the engine by transmitting power of a motor to the engine,
Determine whether the engine start conditions are met,
When it is determined that the engine start condition is satisfied, a field current is supplied to the motor,
Detecting the temperature of the engine,
Based on the detected temperature of the engine, a determination threshold value for determining whether or not the field current has become larger than a current that can generate a torque sufficient to start the engine,
Detecting the field current;
Based on the set determination threshold, it is determined whether or not the detected field current is larger than a current capable of generating a torque sufficient to start the engine,
When it is determined that the field current has become larger than a current that can generate sufficient torque to start the engine, an armature current is supplied to the motor ;
The determination threshold is a determination time for comparing with an elapsed time from the start of energization of the field current,
When the elapsed time from the start of energization of the field current exceeds the determination time, it is determined that the field current is larger than a current capable of generating a torque sufficient to start the engine,
Based on the temperature of the engine, the determination time is set.
The engine starting method characterized by the above-mentioned. An engine starting method for starting the engine by transmitting power of a motor to the engine,
Determine whether the engine start conditions are met,
When it is determined that the engine start condition is satisfied, a field current is supplied to the motor,
Detecting the temperature of the motor;
Based on the detected temperature of the motor, a determination threshold for determining whether or not the field current has become larger than a current capable of generating a torque sufficient to start the engine,
Detecting the field current;
Based on the set determination threshold, it is determined whether or not the detected field current is larger than a current capable of generating a torque sufficient to start the engine,
When it is determined that the field current has become larger than a current that can generate sufficient torque to start the engine, an armature current is supplied to the motor ;
The determination threshold is a determination time for comparing with an elapsed time from the start of energization of the field current,
When the elapsed time from the start of energization of the field current exceeds the determination time, it is determined that the field current is larger than a current capable of generating a torque sufficient to start the engine,
Setting the determination time based on the temperature of the motor;
The engine starting method characterized by the above-mentioned.

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